If animals are allowed to eat as much as they want, the feed consumption is made up of maintenance consumption, productive consumption, and luxury consumption. The maintenance consumption represents the minimum requirement without affording the possibility of weight gain and/or egg production. For these, the productive consumption is required. The luxury consumption is ingested in addition and leads to a further weight gain.
The food requirement of animals is subject to large fluctuations. These depend on the age of the animals, the time of year, the feed composition, the plumage, and the stall climate, i.e. temperature, air humidity, oxygen content, light intensity etc. There exists the corresponding danger than if a given amount of feed per day is used, in order to prevent luxury consumption, the animals receive either too much or too little feed. Too much feed raises costs. The luxury consumption can anyway amount to 5-15%, so that a saving can mean an additional profit of 100%. Hence it happens that, in particular towards the end of the laying period, there exists the danger of the so-called fatty liver syndrome, which leads to bad eggshells and increased losses. As against this, too little feed can reduce the production consumption.
In the raising of young hens it is theoretically possible to supply a given amount of feed per day, in order to prevent luxury consumption, and to accept now and then a restriction of the production consumption, i.e., a reduction in the increase in weight; however, up to now this exact supply presented a considerable technical problem, in particular in the upkeep of laying batteries. Accordingly, luxury consumption in the rearing of young hens is permitted, particularly since the goal of rearing is, anyway, the reaching of a given minimum weight.
In the feeding of laying hens, on the contrary, the provision of a given amount of feed per day is debarred. The animals can enter a dip in production, to overcome which they require, according to circumstances, several days.
A process is already known in which a few hundred laying hens are allowed to eat freely and the feed requirement for the rest of the animals is calculated from the amount of feed consumed, subtracting the percentage of luxury consumption. Apart from the fact that this process is costly in time and work, the problem also arises here of supplying the animals with given amounts of feed. Metering screws are used, which supply the individual cages, and in fact in dependence on the number of animals contained in each cage. The cost of apparatus is considerable, and the plants are correspondingly expensive.